Two-factor authentication (2FA) uses two separate factors to verify access to your account. The first factor is your username and password. The second factor is something that only you have access to, such as your smartphone. This way, an unauthorised person without the authorised smartphone will not be able to access your account or make sensitive changes even if they should be able to guess your username and password.
Using two-factor authentication, you can also change a variety of client data on your own.